When an engaged CEO has a reunion with her student friends, she meets her then-lover and they fall in love again, but she has to make a decision before leaving the town in four days.

The lead up to the point in time that a decision is made, i.e the deliberation, can take a while but the moment of deciding is very short. Is this story about her deliberating whether or not to leave her fiance? Or is this story about her deciding to leave him for another man?
If the former, it will be a low concept slow plot, as DPG suggested, best externalized with side characters and it runs the risk of being melodramatic.
If the latter, then the goal needs to be clarified - what MUST she achieve as a result of her decision to leave the fiance? Moving overseas feels like she's running away from her problems instead of facing them.

Start a new life abroad with or without her old flame? ?He's the cause of the inciting incident. ?How does he figure into her fleeing abroad? ?That needs to be clarified.

(Fleeing to another country seems to me to be a weak choice to solve her predicament. ?But I'll hold fire on that point for now because it's kosher for a protagonist to initially have the wrong objective goal. ?Only to finally realize it, and make a stronger choice.)

I agree with Nir Shelter that "making a decision" is mostly internal. ?The solution to that is ?easy enough: externalize it by having her bounce her decision making process off of reflector characters.

But I diverge on the point that ?her decision "will take very little time to make". ?If it's a true dramatic dilemma , it could take a lot of time to make. ?Because by definition a dilemma is a situation where she must choose between two equally ?desirable options or two equally undesirable options. ?And she must choose either of them. She can't choose to not choose.

And I think it must be a true dilemma in order ?to maximize dramatic tension and suspense. ?If it isn't a true dilemma, if it's easy for her decide to dump her fiancee, cancel the wedding, ?then the plot is about what happens after she makes that decision.

So what is the story about? ?Working through the dilemma and making (finally) a choice? ?Or making an easy choice and acting on the consequences?

Start a new life abroad with or without her old flame? ?He's the cause of the inciting incident. ?How does he figure into her fleeing abroad? ?That needs to be clarified.

(Fleeing to another country seems to me to be a weak choice to solve her predicament. ?But I'll hold fire on that point for now because it's kosher for a protagonist to initially have the wrong objective goal. ?Only to finally realize it, and make a stronger choice.)

I agree with Nir Shelter that "making a decision" is mostly internal. ?The solution to that is ?easy enough: externalize it by having her bounce her decision making process off of reflector characters.

But I diverge on the point that ?her decision "will take very little time to make". ?If it's a true dramatic dilemma , it could take a lot of time to make. ?Because by definition a dilemma is a situation where she must choose between two equally ?desirable options or two equally undesirable options. ?And she must choose either of them. She can't choose to not choose.

And I think it must be a true dilemma in order ?to maximize dramatic tension and suspense. ?If it isn't a true dilemma, if it's easy for her decide to dump her fiancee, cancel the wedding, ?then the plot is about what happens after she makes that decision.

So what is the story about? ?Working through the dilemma and making (finally) a choice? ?Or making an easy choice and acting on the consequences?